In order to improve mirror performance, particularly high energy laser mirrors, it is necessary to cool them and to effectively block heat penetration to the mirror substrate. Substrate growth due to heat penetration to the substrate is a major contributor to total mirror thermal irradiance mapping errors.
Heretofore, conventional channel designs were employed, but they had the drawback of allowing heat penetration to the substrate. Attempts were made to overcome this problem by using a multi-layer heat exchanger to suppress the heat penetration.
Also, heretofore, foam layer type heat exchangers were used. However, this resulted in unacceptably high pressure loss due to its high degree of resistance.
For purposes of suppressing substrate mapping errors, bimaterial mirrors, such as for example silicon with ULE.RTM., Corning Glass Works, have been employed, but they often present the difficult problem of material coefficient of thermal expansion differential generated stress.